Abstract:

Claims:

1-20. (canceled)

21. A polyisocyanate composition comprising(A) at least one polyisocyanate
obtainable by reacting at least one monomeric (cyclo)aliphatic
isocyanate,(B) at least one compound able to accelerate the reaction of
isocyanate groups with isocyanate-reactive groups,(C) at least one
phosphonite, and(D) at least one sterically hindered phenol, which
contains per aromatic ring just one phenolic hydroxy group and in which
at least one ortho-position relative to the functional group has a
tert-butyl group.

22. The polyisocyanate composition according to claim 21, wherein the
monomeric (cyclo)aliphatic isocyanate is selected from the group
consisting of 1,6-hexamethylene diisocyanate,
1,3-bis(isocyanatomethyl)cyclohexane, isophorone diisocyanate,
4,4'-di(isocyanatocyclohexyl)methane, and
2,4'-di(isocyanatocyclo-hexyl)methane.

23. The polyisocyanate composition according to claim 21, wherein the
polyisocyanate (A) comprises at least one of isocyanurate, biuret,
urethane, allophanate and iminooxadiazinedione groups.

24. The polyisocyanate composition according to claim 21, wherein the
polyisocyanate is a polyisocyanate comprising isocyanurate groups having
a viscosity of 600-1500 mPa*s, a low-viscosity urethane, allophanate, or
a combination thereof having a viscosity of 200-1600 mPa*s.

25. The polyisocyanate composition according to claim 21, wherein the
compound (B) is a Lewis-acidic organometallic compound.

27. The polyisocyanate composition according to claim 21, wherein compound
(C) is a phosphonite of the formulaP(OR1)(OR2)(R3),in
whicheach of R1, R2, and R3 is independently,
C1-C18-alkyl, C6-C12-aryl, and C5-C12
cycloalkyl, each optionally substituted by at least one of aryl, alkyl,
aryloxy, alkyloxy, heteroatoms and heterocycles,and said phosphonite is
optionally monocyclic or polycyclic.

28. The polyisocyanate composition according to claim 27, wherein compound
(C) is a phosphonite of the formula ##STR00002## in which R can be
hydrogen or methyl.

29. The polyisocyanate composition according to claim 21, wherein the
compound (D) is 2,6-bis-tert-butyl-4-methylphenol or
3,5-bis(1,1-dimethylethyl)-4-hydroxy-C7-C9 branched alkyl ester of
benzenepropionic acid.

30. The polyisocyanate composition according to claim 21, further
comprising at least one solvent (E) selected from the group consisting of
an aromatic hydrocarbon, a (cyclo)aliphatic hydrocarbon, a ketone, an
ester, an ether, and a carbonate.

31. The polyisocyanate composition according to claim 21, wherein the
polyisocyanate composition, after seven-week storage at 50.degree. C.,
exhibits not more than 30% of the increase in color number, as described
by a APHA color number in accordance with DIN EN 1557, of similar
polyisocyanate compositions in which neither a component (C) nor a
component (D) is present.

32. A method of stabilizing a polyisocyanate composition comprising
polyisocyanate (A) and at least one compound (B) which is able to
accelerate the reaction of isocyanate groups with isocyanate-reactive
groups, which comprises admixing the polyisocyanate composition
additionally with at least one phosphonite (C), and at least one phenol
(D).

33. A process for preparing a polyurethane coating material, which
comprises reacting a polyisocyanate composition according to claim 21
with at least one binder start which contains isocyanate-reactive groups.

35. A process for preparing a polyurethane coating material, which
comprises mixing at least one polyisocyanate first with at least one
compound (B) which is able to accelerate the reaction of isocyanate
groups with isocyanate-reactive groups, at least one phosphonite (C), at
least one phenol and (D) subsequently applying the mixture to the
substrate and curing it.

36. The polyisocyanate composition according to claim 21, further
comprising at least one ofat least one acidic stabilizer, anda further
coating additive.

37. The polyisocyanate composition according to claim 25, wherein the
Lewis-acidic organometallic compound comprises a metal selected from the
group consisting tin and zinc.

38. The polyisocyanate composition according to claim 21, further
comprising at least one solvent (E) selected from the group consisting of
a distillation cut of aromatic hydrocarbons and a dialkyl ketone, wherein
said distillation cut of aromatic hydrocarbons has C9 and C10
aromatic hydrocarbons as a main component.

39. The method according to claim 32, further comprising admixing at least
one solvent (E), at least one further coating additive (F), or a
combination thereof.

Description:

[0002]WO 2005/089085 describes polyisocyanate compositions as curing
agents for 2K (two component) polyurethane coating materials that in
addition to a catalyst for the reaction between isocyanate groups and
groups reactive therewith comprises a stabilizer mixture selected from
hindered phenols and secondary arylamines and also organophosphites, more
particularly trialkyl phosphites. Explicitly disclosed in the examples is
a polyisocyanate composition, the isocyanurate Tolonate HDT, with
dibutyltin dilaurate as catalyst in butyl acetate/methyl amyl
ketone/xylene 1:1:0.5.

[0003]A disadvantage of phosphites, however, particularly of trialkyl
phosphites and more particularly of tributyl phosphite, is that they have
a very unpleasantly reeking odor. In terms of toxicological
classification, tributyl phosphite is injurious to health on contact with
the skin, and corrosive. Triphenyl phosphite is irritant to eyes and
skin, and highly toxic for aquatic organisms. Phosphites, moreover, are
sensitive to moisture. Consequently these compounds, at least before and
during incorporation into polyisocyanate compositions, represent a
problem from the standpoints of health, occupational hygiene, and
processing. Whereas the antioxidative action of aromatic phosphites is
lower than that of their aliphatic counterparts, the availability of the
aliphatic phosphites is poorer.

[0004]U.S. Pat. No. 6,376,584 B1 describes various stabilizers for use in
polyurethane compositions in which polyisocyanates are reacted with
polyols in the presence of dibutyltin dilaurate.

[0005]Not disclosed are the stabilization problems that arise when
polyisocyanate compositions are mixed with a catalyst and stored.

[0006]U.S. Pat. No. 7,122,588 B2 describes coating materials, including
polyurethane coating materials, which are stabilized with esters of
hypophosphorous acid for the purpose of extending their life and against
discoloration.

[0007]Not disclosed are the stabilization problems which arise when
polyisocyanate compositions are mixed with a catalyst and stored.
Moreover, the stabilization described therein is still not sufficient,
and so there continues to be a need for improved stabilization.

[0008]EP 735027 A1 describes a process for preparing uretdiones with
enhanced color quality by reacting (cyclo)aliphatic diisocyanates with
catalysis by pyridine derivatives which additionally contain 0.1%-4% of
trivalent phosphorus compounds of a general formula. Explicitly
disclosed, however, are only phosphines, phosphites and phosphonates.
Following the preparation, these phosphorus compounds are distilled off
together with the unreacted isocyanate. No addition of phosphites for the
purpose of stabilizing polyisocyanates is described, especially not in
the presence of urethanization catalysts.

[0009]DE 19630903 describes the stabilization of isocyanates with various
phosphorus compounds and phenols.

[0010]Not described in each case is the presence of catalysts for the
reaction between isocyanate groups and groups reactive therewith.

[0011]It is an object of the present invention to provide further
storage-stable polyisocyanate compositions which already include a
catalyst for the reaction between isocyanate groups and groups reactive
therewith and are color-stable, and whose stabilizers, in terms of odor,
toxicology and/or moisture sensitivity, allow unproblematic occupational
hygiene and health, and whose stabilizing action is at least comparable
with that of the prior art. The stabilizing action ought to be
independent of the origin of the monomeric isocyanate.

[0012]This object has been achieved by polyisocyanate compositions
comprising [0013](A) at least one polyisocyanate obtainable by reacting
at least one monomeric isocyanate, [0014](B) at least one compound able
to accelerate the reaction of isocyanate groups with isocyanate-reactive
groups, [0015](C) at least one phosphonite, [0016](D) optionally at least
one sterically hindered phenol, [0017](E) optionally at least one
solvent, [0018](F) optionally at least one acidic stabilizer, [0019](G)
optionally other, typical coatings additives.

[0020]Polyisocyanate compositions of this kind can be reacted directly
with components comprising isocyanate-reactive groups in polyurethane
coating materials and feature good color stability on storage.

[0021]In one preferred embodiment the polyisocyanate compositions of the
invention, after being stored for seven weeks at 50° C., exhibit
not more than 30% of the increase in color number (APHA color number in
accordance with DIN EN 1557) of similar polyisocyanate compositions of
the prior art in which neither a component (C) nor a component (D) is
present.

[0022]The monomeric isocyanates used may be aromatic, aliphatic or
cycloaliphatic, preferably aliphatic or cycloaliphatic, which is referred
to for short in this text as (cyclo)aliphatic; aliphatic isocyanates are
particularly preferred.

[0023]Aromatic isocyanates are those which comprise at least one aromatic
ring system, in other words not only purely aromatic compounds but also
araliphatic compounds.

[0024]Cycloaliphatic isocyanates are those which comprise at least one
cycloaliphatic ring system.

[0026]The monomeric isocyanates are preferably diisocyanates, which carry
precisely two isocyanate groups. They can, however, in principle also be
monoisocyanates, having one isocyanate group.

[0027]In principle, higher isocyanates having on average more than 2
isocyanate groups are also contemplated. Suitability therefor is
possessed for example by triisocyanates, such as triisocyanatononane,
2'-isocyanatoethyl 2,6-diisocyanatohexanoate,
2,4,6-triiso-cyanatotoluene, triphenylmethane triisocyanate or
2,4,4'-triisocyanatodiphenyl ether, or the mixtures of diisocyanates,
triisocyanates, and higher polyisocyanates that are obtained, for
example, by phosgenation of corresponding aniline/formaldehyde
condensates and represent methylene-bridged polyphenyl polyisocyanates.

[0028]These monomeric isocyanates do not contain any substantial products
of reaction of the isocyanate groups with themselves.

[0030]Particular preference is given to hexamethylene 1,6-diisocyanate,
1,3-bis(isocyanato-methyl)cyclohexane, isophorone diisocyanate, and 4,4'-
or 2,4'-di(isocyanato-cyclohexyl)methane, very particular preference to
isophorone diisocyanate and hexamethylene 1,6-diisocyanate, and especial
preference to hexamethylene 1,6-diisocyanate.

[0031]Mixtures of said isocyanates may also be present.

[0032]Isophorone diisocyanate is usually in the form of a mixture,
specifically a mixture of the cis and trans isomers, generally in a
proportion of about 60:40 to 80:20 (w/w), preferably in a proportion of
about 70:30 to 75:25, and more preferably in a proportion of
approximately 75:25.

[0033]Dicyclohexylmethane 4,4'-diisocyanate may likewise be in the form of
a mixture of the different cis and trans isomers.

[0034]For the present invention it is possible to use not only those
diisocyanates obtained by phosgenating the corresponding amines but also
those prepared without the use of phosgene, i.e., by phosgene-free
processes. According to EP-A-0 126 299 (U.S. Pat. No. 4,596,678),
EP-A-126 300 (U.S. Pat. No. 4,596,679), and EP-A-355 443 (U.S. Pat. No.
5,087,739), for example, (cyclo)aliphatic diisocyanates, such as
hexamethylene 1,6-diisocyanate (HDI), isomeric aliphatic diisocyanates
having 6 carbon atoms in the alkylene radical, 4,4'- or
2,4'-di(isocyanatocyclohexyl)methane, and
1-isocyanato-3-isocyanatomethyl-3,55-trimethylcyclohexane (isophorone
diisocyanate or IPDI) can be prepared by reacting the (cyclo)aliphatic
diamines with, for example, urea and alcohols to give (cyclo)aliphatic
biscarbamic esters and subjecting said esters to thermal cleavage into
the corresponding diisocyanates and alcohols. The synthesis takes place
usually continuously in a circulation process and in the presence, if
appropriate, of N-unsubstituted carbamic esters, dialkyl carbonates, and
other by-products recycled from the reaction process. Diisocyanates
obtained in this way generally contain a very low or even unmeasurable
fraction of chlorinated compounds, which is advantageous, for example, in
applications in the electronics industry.

[0035]In one embodiment of the present invention the isocyanates used have
a total hydrolyzable chlorine content of less than 200 ppm, preferably of
less than 120 ppm, more preferably less than 80 ppm, very preferably less
than 50 ppm, in particular less than 15 ppm, and especially less than 10
ppm. This can be measured by means, for example, of ASTM specification
D4663-98. Of course, though, monomeric isocyanates having a higher
chlorine content can also be used, of up to 500 ppm, for example.

[0036]It will be appreciated that it is also possible to employ mixtures
of those monomeric isocyanates which have been obtained by reacting the
(cyclo)aliphatic diamines with, for example, urea and alcohols and
cleaving the resulting (cyclo)aliphatic biscarbamic esters, with those
diisocyanates which have been obtained by phosgenating the corresponding
amines.

[0037]The polyisocyanates (A) which can be formed by oligomerizing the
monomeric isocyanates are generally characterized as follows:

[0038]The average NCO functionality of such compounds is in general at
least 1.8 and can be up to 8, preferably 2 to 5, and more preferably 2.4
to 4.

[0039]The isocyanate group content after oligomerization, calculated as
NCO=42 g/mol, is generally from 5% to 25% by weight unless otherwise
specified.

[0040]The polyisocyanates (A) are preferably compounds as follows:
[0041]1) Polyisocyanates containing isocyanurate groups and derived from
aromatic, aliphatic and/or cycloaliphatic diisocyanates. Particular
preference is given in this context to the corresponding aliphatic and/or
cycloaliphatic isocyanatoisocyanurates and in particular to those based
on hexamethylene diisocyanate and isophorone diisocyanate. The
isocyanurates present are, in particular, trisisocyanatoalkyl and/or
trisisocyanatocycloalkyl isocyanurates, which constitute cyclic trimers
of the diisocyanates, or are mixtures with their higher homologs
containing more than one isocyanurate ring. The isocyanatoisocyanurates
generally have an NCO content of 10% to 30% by weight, in particular 15%
to 25% by weight, and an average NCO functionality of 2.6 to 8. [0042]2)
Polyisocyanates containing uretdione groups and having aromatically,
aliphatically and/or cycloaliphatically attached isocyanate groups,
preferably aliphatically and/or cycloaliphatically attached, and in
particular those derived from hexamethylene diisocyanate or isophorone
diisocyanate. Uretdione diisocyanates are cyclic dimerization products of
diisocyanates. The polyisocyanates containing uretdione groups are
obtained in the context of this invention as a mixture with other
polyisocyanates, more particularly those specified under 1). For this
purpose the diisocyanates can be reacted under reaction conditions under
which not only uretdione groups but also the other polyisocyanates are
formed, or the uretdione groups are formed first of all and are
subsequently reacted to give the other polyisocyanates, or the
diisocyanates are first reacted to give the other polyisocyanates, which
are subsequently reacted to give products containing uretdione groups.
[0043]3) Polyisocyanates containing biuret groups and having
aromatically, cyclo-aliphatically or aliphatically attached, preferably
cycloaliphatically or aliphatically attached, isocyanate groups,
especially tris(6-isocyanatohexyl)biuret or its mixtures with its higher
homologs. These polyisocyanates containing biuret groups generally have
an NCO content of 18% to 22% by weight and an average NCO functionality
of 2.8 to 6. [0044]4) Polyisocyanates containing urethane and/or
allophanate groups and having aromatically, aliphatically or
cycloaliphatically attached, preferably aliphatically or
cycloaliphatically attached, isocyanate groups, such as may be obtained,
for example, by reacting excess amounts of diisocyanate, such as of
hexamethylene diisocyanate or of isophorone diisocyanate, with mono- or
polyhydric alcohols (A). These polyisocyanates containing urethane and/or
allophanate groups generally have an NCO content of 12% to 24% by weight
and an average NCO functionality of 2.5 to 4.5. Polyisocyanates of this
kind containing urethane and/or allophanate groups may be prepared
without catalyst or, preferably, in the presence of catalysts, such as
ammonium carboxylates or ammonium hydroxides, for example, or
allophanatization catalysts, such as Zn(II) compounds, for example, in
each case in the presence of monohydric, dihydric or polyhydric,
preferably monohydric, alcohols. [0045]5) Polyisocyanates comprising
oxadiazinetrione groups, derived preferably from hexamethylene
diisocyanate or isophorone diisocyanate. Polyisocyanates of this kind
comprising oxadiazinetrione groups are accessible from diisocyanate and
carbon dioxide. [0046]6) Polyisocyanates comprising iminooxadiazinedione
groups, derived preferably from hexamethylene diisocyanate or isophorone
diisocyanate. Polyisocyanates of this kind comprising
iminooxadiazinedione groups are preparable from diisocyanates by means of
specific catalysts. [0047]7) Uretonimine-modified polyisocyanates.
[0048]8) Carbodiimide-modified polyisocyanates. [0049]9) Hyperbranched
polyisocyanates, of the kind known for example from DE-A1 10013186 or
DE-A1 10013187. [0050]10) Polyurethane-polyisocyanate prepolymers, from
di- and/or polyisocyanates with alcohols. [0051]11)
Polyurea-polyisocyanate prepolymers. [0052]12) The polyisocyanates
1)-11), preferably 1), 3), 4), and 6), can be converted, following their
preparation, into polyisocyanates containing biuret groups or
urethane/allophanate groups and having aromatically, cycloaliphatically
or aliphatically attached, preferably (cyclo)aliphatically attached,
isocyanate groups. The formation of biuret groups, for example, is
accomplished by addition of water or by reaction with amines. The
formation of urethane and/or allophanate groups is accomplished by
reaction with monohydric, dihydric or polyhydric, preferably monohydric,
alcohols, in the presence if appropriate of suitable catalysts. These
polyisocyanates containing biuret or urethane/allophanate groups
generally have an NCO content of 18% to 22% by weight and an average NCO
functionality of 2.8 to 6. [0053]13) Hydrophilically modified
polyisocyanates, i.e., polyisocyanates which as well as the groups
described under 1-12 also comprise groups which result formally from
addition of molecules containing NCO-reactive groups and hydrophilizing
groups to the isocyanate groups of the above molecules. The latter groups
are nonionic groups such as alkylpolyethylene oxide and/or ionic groups
derived from phosphoric acid, phosphonic acid, sulfuric acid or sulfonic
acid, and/or their salts. [0054]14) Modified polyisocyanates for dual
cure applications, i.e., polyisocyanates which as well as the groups
described under 1-13 also comprise groups resulting formally from
addition of molecules containing NCO-reactive groups and UV-crosslinkable
or actinic-radiation-crosslinkable groups to the isocyanate groups of the
above molecules. These molecules are, for example, hydroxyalkyl
(meth)acrylates and other hydroxylvinyl compounds.

[0055]The diisocyanates or polyisocyanates recited above may also be
present at least partly in blocked form.

[0056]Classes of compounds used for blocking are described in D. A. Wicks,
Z. W. Wicks, Progress in Organic Coatings, 36, 148-172 (1999), 41, 1-83
(2001) and also 43, 131-140 (2001).

[0058]In one preferred embodiment of the present invention the
polyisocyanate (A) is selected from the group consisting of
isocyanurates, biurets, urethanes, and allophanates, preferably from the
group consisting of isocyanurates, urethanes, and allophanates, more
preferably from the group consisting of isocyanurates and allophanates;
in particular it is a polyisocyanate containing isocyanurate groups.

[0060]In one further particularly preferred embodiment the polyisocyanate
(A) encompasses a mixture of polyisocyanates comprising isocyanurate
groups and obtained from 1,6-hexamethylene diisocyanate and from
isophorone diisocyanate.

[0062]In this specification, unless noted otherwise, the viscosity is
reported at 23° C. in accordance with DIN EN ISO 3219/A.3 in a
cone/plate system with a shear rate of 1000 s-1.

[0063]The process for preparing the polyisocyanates may take place as
described in the unpublished European patent application with the
application number 06125323.3 and the filing date of Dec. 4, 2006,
especially from page 20 line 21 to page 27 line 15 therein, which is
hereby made part of the present specification by reference.

[0064]The reaction can be discontinued, for example, as described therein
from page 31 line 19 to page 31 line 31, and working up may take place as
described therein from page 31 line 33 to page 32 line 40, which in each
case is hereby made part of the present specification by reference.

[0065]The reaction can alternatively be discontinued as described in WO
2005/087828 from page 11 line 12 to page 12 line 5, which is hereby made
part of the present specification by reference.

[0066]In the case of thermally labile catalysts it is also possible,
furthermore, to discontinue the reaction by heating the reaction mixture
to a temperature above at least 80° C., preferably at least
100° C., more preferably at least 120° C. Generally it is
sufficient for this purpose to heat the reaction mixture, in the way
which is necessary at the working-up stage in order to separate the
unreacted isocyanate, by distillation.

[0067]In the case both of thermally non-labile catalysts and of thermally
labile catalysts, the possibility exists of terminating the reaction at
relatively low temperatures by addition of deactivators. Examples of
suitable deactivators are hydrogen chloride, phosphoric acid, organic
phosphates, such as dibutyl phosphate or diethylhexyl phosphate,
carbamates such as hydroxyalkyl carbamate, or organic carboxylic acids.

[0068]These compounds are added neat or diluted in a suitable
concentration as necessary to discontinue the reaction.

[0069]Compounds (B), which are able to accelerate the reaction of
isocyanate groups with isocyanate-reactive groups, are those compounds
which, by their presence in a reactant mixture, result in a higher
fraction of reaction products containing urethane groups than does the
same reactant mixture in their absence, under the same reaction
conditions.

[0079]Preferred here are cesium carboxylates in which the anion conforms
to the formulae (OCnH2n-1)-- and also
(Cn+1H2n-2O2)2-, with n being 1 to 20. Particularly
preferred cesium salts contain monocarboxylate anions of the general
formula (OCnH2n+1)--, with n standing for the numbers 1 to 20.
Particular mention in this context is deserved by formate, acetate,
propionate, hexanoate, and 2-ethylhexanoate.

[0081]Particular preference, however, is given to dibutyltin dilaurate.

[0082]Phosphonites (C) are compounds which meet the formula

P(OR1)(OR2)(R3),

in which

[0083]R1, R2, and R3 each independently can be
C1-C18 alkyl, C6-C12 aryl, and
C5-C12-cycloalkyl, it being possible for each of the stated
radicals to be substituted by aryl, alkyl, aryloxy, alkyloxy, heteroatoms
and/or heterocycles.

[0085]By "polycyclic" phosphonites are meant those which within one
molecule carry two or more phosphonite groups, i.e., singularly,
organically substituted phosphorus atoms which in turn carry two
organically substituted oxygen atoms.

[0092]Examples of other compounds of this type and also corresponding
bis-thio compounds are found in U.S. Pat. No. 4,075,163, hereby made part
of the present specification by reference.

[0093]For the case of a dinuclear phosphonite it is preferred for the
phosphonite groups to be connected to one another via a 4,4'-biphenylene
unit.

[0094]Preference is given to the compound
tetrakis(2,4-di-tert-butylphenyl)-4,4'-diphenylene diphosphonite [CAS No.
119345-01-6], which is available commercially, for example, under the
trade name Irgafos® P-EPQ from Ciba Spezialitatenchemie and
Hostanox® P-EPQ from Clariant, and which has the following structural
formula (where R═H):

##STR00001##

[0095]Tetrakis(2,4-di-tert-butylphenyl)-4,4'-diphenylene diphosphonite is
readily available industrially and is used as an antioxidant for
thermoplastics.

[0096]Tetrakis(2,4-di-tert-butylphenyl)-4,4'-diphenylene diphosphonite is
highly soluble in organic solvents. As a result of its preparation,
however, it comprises chlorine-containing secondary components, which can
lead to hazing. These chlorine-containing secondary components can be
extracted very largely by means, for example, of extraction of these
compounds with water from an organic solution, as for example with hexane
or methylene chloride against water or saturated sodium chloride
solution, and can subsequently be dried, for example, over magnesium
sulfate.

[0097]Such purified forms of this compound are especially preferred for
the process of the invention, since hazing in the polyisocyanate
compositions of the invention or in the completed coating materials is
unwanted.

[0098]Preference is also given to the compound
tetrakis(2,4-di-tert-butyl-5-methylphenyl)[1,1-biphenyl]-4,4'-diylbisphos-
phonite (or alternatively tetrakis(2,4-di-tert-butyl-5-methylphenyl)
4,4'-diphenylene diphosphonite), which is sold under the trade name GSY-P
101 by API Corporation or Yoshitomi, and has the above structural formula
with R=methyl.

[0099]The two last-mentioned compounds are toxicologically unproblematic,
are stable to hydrolysis and are almost odorless as compared with
phosphites, and consequently are advantageous from the standpoints of
health and occupational hygiene.

[0100]The phosphonite in this invention functions primarily as a secondary
antioxidant. These are typically understood by the skilled worker to be
compounds which prevent the formation of free radicals, more particularly
by scavenging and/or breaking down peroxides.

[0101]Optionally it is possible for at least one phenol to be present,
preferably at least one sterically hindered phenol (D); with preference
there is at least one, more preferably just one, phenol (D) present.
Phenols in the sense of the invention have the function of a primary
antioxidant. This is typically understood by the skilled worker to refer
to compounds which scavenge free radicals.

[0103]The compounds in question are preferably phenols which on the
aromatic ring have just one phenolic hydroxy group, and more preferably
those which in ortho-position, very preferably in ortho- and
para-position to the phenolic hydroxy group, have any desired
substituent, preferably an alkyl group.

[0104]Phenols of this kind may also be parts of a polyphenolic system
having two or more phenol groups, such as pentaerythritol
tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (e.g.,
Irganox® 1010), Irganox® 1330,
1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,-
5H)trione (e.g., Irganox® 3114), each products of Ciba
Spezialitatenchemie.

[0105]Corresponding products are available, for example, under the trade
names Irganox® (Ciba Spezialitatenchemie), Sumilizer® from
Sumitomo, Lowinox® from Great Lakes, and Cyanox® from Cytec.

[0107]It is possible as well, furthermore, optionally for a solvent or
solvent mixture (E) to be present.

[0108]Solvents which can be used are those which contain no groups that
are reactive toward isocyanate groups or blocked isocyanate groups, and
in which the polyisocyanates are soluble to an extent of at least 10%,
preferably at least 25%, more preferably at least 50%, very preferably at
least 75%, more particularly at least 90%, and especially at least 95% by
weight.

[0110]Preferred aromatic hydrocarbon mixtures are those which comprise
predominantly aromatic C7- to C14 hydrocarbons and may
encompass a boiling range from 110 to 300° C.; particular
preference is given to toluene, o-, m- or p-xylene, trimethylbenzene
isomeres, tetramethylbenzene isomers, ethylbenzene, cumene,
tetrahydronaphthalene and mixtures comprising them.

[0111]Examples thereof are the Solvesso® products from Exxon Mobil
Chemical, especially Solvesso® 100 (CAS No. 64742-95-6, predominantly
C9 and C10 aromatics, boiling range about 154-178° C.),
150 (boiling range about 182-207° C.), and 200 (CAS No.
64742-94-5), and also the Shellsol® products from Shell, Caromax®
(e.g., Caromax® 18) from Petrochem Carless and Hydrosol from DHC
(e.g., as Hydrosol® A 170). Hydrocarbon mixtures comprising
paraffins, cycloparaffins, and aromatics are also available commercially
under the names Kristalloel (for example, Kristalloel 30, boiling range
about 158-198° C. or Kristalloel 60: CAS No. 64742-82-1), white
spirit (for example likewise CAS No. 64742-82-1) or solvent naphtha
(light: boiling range about 155-180° C., heavy: boiling range
about 225-300° C.). The aromatics content of such hydrocarbon
mixtures is generally more than 90%, preferably more than 95%, more
preferably more than 98%, and very preferably more than 99% by weight. It
may be advisable to use hydrocarbon mixtures having a particularly
reduced naphthalene content.

[0117]Surprisingly it has been found that the solvents are differently
problematic in relation to the stated object. Polyisocyanate compositions
as per the patent which comprise ketones or mixtures of aromatics
(solvent naphtha mixtures, for example) are particularly critical in
respect of development of color number on storage. In contrast, esters,
ethers, and certain aromatics such as xylene or its isomer mixtures are
less problematic. This is surprising insofar as xylenes, in the same way
as the mixtures of aromatics, likewise carry benzylic hydrogen atoms,
which could play a part in the development of color. A further factor is
that solvent naphtha mixtures, depending on the source and storage time,
can have significantly different effects on color number drift if used in
the polyisocyanate compositions.

[0118]Optionally it is also possible in addition for a further stabilizing
compound to be added in the form of at least one, preferably just one,
acidic stabilizer (F). The compounds in question are Bronsted acids.

[0120]As acidic stabilizers it is preferred to use aliphatic
monocarboxylic acids and 1 to 8 C atoms, such as formic acid and acetic
acid, for example, aliphatic dicarboxylic acids having 2 to 6 C atoms,
such as oxalic acid, for example, and more particularly 2-ethylhexanoic
acid, chloropropionoic acid and/or methoxy acetic acid.

[0123]These can be employed alone or together with suitable free-radical
scavengers, examples being sterically hindered amines (often also
identified as HALS or HAS compounds; hindered amine (light) stabilizers)
such as 2,2,6,6-tetramethylpiperidine, 2,6-di-tert-butylpiperidine or
derivatives thereof, e.g., bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate.
They are obtainable, for example, as Tinuvin® products and
Chimassorb® products from Ciba Spezialitatenchemie. Preference in
joint use with Lewis acids, however, is given to those hindered amines
which are N-alkylated, examples being
bis(1,2,2,6,6-pentamethyl-4-piperidinyl)
[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butylmalonate (e.g.,
Tinuvin® 144 from Ciba Spezialitatenchemie); a mixture of
bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate and
methyl(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate (e.g., Tinuvin®
292 from Ciba Spezialitatenchemie); or which are N--(O-alkylated), such
as, for example, decanedioic acid,
bis(2,2,6,6-tetramethyl-1-(octyloxy)-4-piperidinyl) ester, reaction
products with 1,1-dimethylethyl hydroperoxide and octane (e.g.,
Tinuvin® 123 from Ciba Spezialitatenchemie).

[0124]UV stabilizers are used typically in amounts of 0.1% to 5.0% by
weight, based on the solid components present in the preparation.

[0125]Suitable thickeners include, in addition to free-radically
(co)polymerized (co)polymers, typical organic and inorganic thickeners
such as hydroxymethylcellulose or bentonite.

[0126]Chelating agents which can be used include, for example,
ethylenediamineacetic acid and salts thereof and also β-diketones.

[0127]As component (H) in addition it is possible for fillers, dyes and/or
pigments to be present.

[0128]Pigments in the true sense are, according to CD Rompp Chemie
Lexikon--Version 1.0, Stuttgart/New York: Georg Thieme Verlag 1995, with
reference to DIN 55943, particulate "colorants that are organic or
inorganic, chromatic or achromatic and are virtually insoluble in the
application medium".

[0130]Examples of pigments in the true sense comprise any desired systems
of absorption pigments and/or effect pigments, preferably absorption
pigments. There are no restrictions whatsoever on the number and
selection of the pigment components. They may be adapted as desired to
the particular requirements, such as the desired perceived color, for
example, as described in step a), for example. It is possible for example
for the basis to be all the pigment components of a standardized mixer
system.

[0131]Effect pigments are all pigments which exhibit a platelet-shaped
construction and give a surface coating specific decorative color
effects. The effect pigments are, for example, all of the pigments which
impart effect and can be used typically in vehicle finishing and
industrial coatings. Examples of such effect pigments are pure metallic
pigments, such as aluminum, iron or copper pigments; interference
pigments, such as titanium dioxide-coated mica, iron oxide-coated mica,
mixed oxide-coated mica (e.g., with titanium dioxide and Fe2O3
or titanium dioxide and Cr2O3), metal oxide-coated aluminum; or
liquid-crystal pigments, for example.

[0135]Coloristically inert fillers are all substances/compounds which on
the one hand are coloristically inactive, i.e., exhibit a low intrinsic
absorption and have a refractive index similar to that of the coating
medium, and which on the other hand are capable of influencing the
orientation (parallel alignment) of the effect pigments in the surface
coating, i.e., in the applied coating film, and also properties of the
coating or of the coating compositions, such as hardness or rheology, for
example. Inert substances/compounds which can be used are given by way of
example below, but without restricting the concept of coloristically
inert, topology-influencing fillers to these examples. Suitable inert
fillers meeting the definition may be, for example, transparent or
semitransparent fillers or pigments, such as silica gels, blanc fixe,
kieselguhr, talc, calcium carbonates, kaolin, barium sulfate, magnesium
silicate, aluminum silicate, crystalline silicon dioxide, amorphous
silica, aluminum oxide, microspheres or hollow microspheres made, for
example, of glass, ceramic or polymers, with sizes of 0.1-50 μm, for
example. Additionally as inert fillers it is possible to employ any
desired solid inert organic particles, such as urea-formaldehyde
condensates, micronized polyolefin wax and micronized amide wax, for
example. The inert fillers can in each case also be used in a mixture. It
is preferred, however, to use only one filler in each case.

[0137]In one preferred form, polyisocyanates (A) are made available for
further processing in a first step in a blend with phosphonite (C),
optionally hindered phenol (D), optionally solvent(s) (E), optionally
acidic stabilizer (F), and optionally additives (G). The amount of
polyisocyanate in this case is typically more than 50%, in particular
65-99.99% by weight. These mixtures are then converted, in a second step,
into the polyisocyanate compositions of the invention, by addition
of--where appropriate--further of components (B) to (G), and also,
optionally, (H).

[0138]Preferred solvents for premixes of this first step are n-butyl
acetate, ethyl acetate, 1-methoxyprop-2-yl acetate, 2-methoxyethyl
acetate, and mixtures thereof, especially with the aromatic hydrocarbon
mixtures set out above.

[0139]Mixtures of this kind can be produced in a volume ratio of 5:1 to
1:5, preferably in a volume ratio of 4:1 to 1:4, more preferably in a
volume ratio of 3:1 to 1:3, and very preferably in a volume ratio of 2:1
to 1:2.

[0141]The constitution of the polyisocyanate compositions of the invention
is for example as follows:

(A) 20% to 99.998%, preferably 30% to 90%, more preferably 40-80% by
weight,(B) 10 to 10 000 ppm, preferably 20 to 5000 ppm, more preferably
30 to 2000 ppm, and very preferably 50 to 1000 ppm by weight,(C) 10 to
5000 ppm, preferably 20 to 2000 ppm, more preferably 50 to 1000 ppm, and
very preferably 100 to 1000 ppm by weight,(D) 0 to 5000 ppm, preferably
10 to 2000 ppm, more preferably 20 to 600 ppm, and very preferably 50 to
200 ppm by weight, and(E) 0% to 80%, preferably 10-70%, more preferably
20% to 60% by weight,(F) 0-5000 ppm, preferably 20 to 500 ppm by
weight,(G)0-5% additives,with the proviso that the sum always makes 100%
by weight.

[0142]Where components (H) are present, they are not included in the
composition of components (A) to (G).

[0143]The polyisocyanate compositions of the invention can be used with
advantage as curing agent components additionally to at least one binder
in polyurethane coating materials.

[0144]The reaction with binders may take place, where appropriate, after a
long period of time, necessitating storage of the polyisocyanate
composition accordingly. Although polyisocyanate composition is stored
preferably at room temperature, it can also be stored at higher
temperatures. In industry, heating of such polyisocyanate compositions to
40° C., 60° C. and even up to 80° C. is entirely
possible.

[0147]Additionally the binders may have an acid number in accordance with
DIN EN ISO 3682 of up to 200 mg KOH/g, preferably up to 150 and more
preferably up to 100 mg KOH/g.

[0148]Polyacrylate polyols preferably have a molecular weight Mn of
at least 1000, more preferably at least 2000, and very preferably at
least 5000 g/mol. The molecular weight Mn, may in principle have no
upper limit, and may preferably be up to 200 000, more preferably up to
100 000, and very preferably up to 50 000 g/mol.

[0151]The hydroxyl-bearing monomers are used in the copolymerization in a
mixture of other polymerizable monomers, preferably free-radically
polymerizable monomers, preferably those composed to an extent of more
than 50% by weight of C1-C20, preferably C1 to C4
alkyl (meth)acrylate, (meth)acrylic acid, vinylaromatics having up to 20
C atoms, vinyl esters of carboxylic acids comprising up to 20 C atoms,
vinyl halides, nonaromatic hydrocarbons having 4 to 8 C atoms and 1 or 2
double bonds, unsaturated nitriles, and mixtures thereof. Particular
preference is given to the polymers composed to an extent of more than
60% by weight of C1-C10 alkyl (meth)acrylates, styrene and its
derivatives, vinylimidazol or mixtures thereof.

[0153]Further polymers are, for example, polyesterols, as are obtainable
by condensing polycarboxylic acids, especially dicarboxylic acids, with
polyols, especially diols. In order to ensure a polyester polyol
functionality that is appropriate for the polymerization, use is also
made in part of triols, tetrols, etc, and also triacids etc.

[0154]Polyester polyols are known for example from Ullmanns Encyklopadie
der technischen Chemie, 4th edition, volume 19, pp. 62 to 65. It is
preferred to use polyester polyols which are obtained by reacting
dihydric alcohols with dibasic carboxylic acids. In lieu of the free
polycarboxylic acids it is also possible to use the corresponding
polycarboxylic anhydrides or corresponding polycarboxylic esters of lower
alcohols or mixtures thereof to prepare the polyester polyols. The
polycarboxylic acids may be aliphatic, cycloaliphatic, aromatic or
heterocyclic and may if appropriate be substituted, by halogen atoms for
example, and/or unsaturated. Examples thereof that may be mentioned
include the following:

[0157]Preferred alcohols are those of the general formula
HO--(CH2)x--OH, where x is a number from 1 to 20, preferably an
even number from 2 to 20. Preferred are ethylene glycol, butane-1,4-diol,
hexane-1,6-diol, octane-1,8-diol and dodecane-1,12-diol. Additionally
preferred is neopentyl glycol.

[0158]Also suitable, furthermore, are polycarbonate diols of the kind
obtainable, for example, by reacting phosgene with an excess of the low
molecular mass alcohols specified as synthesis components for the
polyester polyols.

[0159]Also suitable are lactone-based polyester diols, which are
homopolymers or copolymers of lactones, preferably hydroxy-terminated
adducts of lactones with suitable difunctional starter molecules.
Suitable lactones are preferably those which derive from compounds of the
general formula HO--(CH2)z--COOH, where z is a number from 1 to
20 and where one H atom of a methylene unit may also have been
substituted by a C1 to C4 alkyl radical. Examples are
ε-caprolactone, β-propiolactone, gamma-butyrolactone and/or
methyl-ε-caprolactone, 4-hydroxybenzoic acid,
6-hydroxy-2-naphthoic acid or pivalolactone, and mixtures thereof.
Examples of suitable starter components include the low molecular mass
dihydric alcohols specified above as a synthesis component for the
polyester polyols. The corresponding polymers of ε-caprolactone
are particularly preferred. Lower polyester diols or polyether diols as
well can be used as starters for preparing the lactone polymers. In lieu
of the polymers of lactones it is also possible to use the corresponding,
chemically equivalent polycondensates of the hydroxycarboxylic acids
corresponding to the lactones.

[0160]Also suitable as polymers, furthermore, are polyetherols, which are
prepared by addition reaction of ethylene oxide, propylene oxide or
butylene oxide with H-active components. Polycondensates of butanediol
are also suitable.

[0161]In addition it is possible to use hydroxy-functional carboxylic
acids, such as dimethylolpropionic acid or dimethylolbutanoic acid, for
example.

[0162]The polymers can of course also be compounds containing primary or
secondary amino groups.

[0163]For this purpose, polyisocyanate composition and binder are mixed
with one another in a molar ratio of isocyanate groups to
isocyanate-reactive groups of 0.1:1 to 10:1, preferably 0.2:1 to 5:1,
more preferably 0.3:1 to 3:1, very preferably 0.5:1 to 2:1, more
particularly 0.8:1 to 1.2:1, and especially 0.9:1 to 1.1:1, it being
possible if desired to mix in further, typical coatings constituents, and
the resulting mixture is applied to the substrate.

[0164]Subsequently the coating-material mixture is cured at ambient
temperature to 140° C., preferably 20 to 80° C., more
preferably up to 60° C.

[0165]Depending on temperature, this usually takes not more than 12 hours,
preferably up to 8 hours, more preferably up to 6, very preferably up to
4, and in particular up to 3 hours.

[0166]The substrates are coated by typical methods known to the skilled
worker, with at least one coating composition being applied in the
desired thickness to the substrate to be coated, and any volatile
constituents of the coating composition being removed, if appropriate
with heating. This operation may if desired be repeated one or more
times. Application to the substrate may take place in a known way, as for
example by spraying, troweling, knifecoating, brushing, rolling,
rollercoating, flowcoating, laminating, injection backmolding or
coextruding.

[0167]The thickness of a film of this kind for curing may be from 0.1
μm up to several mm, preferably from 1 to 2000 μm, more preferably
5 to 200 μm, very preferably from 5 to 60 μm (based on the coating
material in the state in which the solvent has been removed from the
coating material).

[0168]Additionally provided by the present invention are substrates coated
with a multicoat paint system of the invention.

[0170]The two-component coating compositions and coating formulations
obtained are suitable for coating substrates such as wood, wood veneer,
paper, cardboard, paperboard, textile, film, leather, nonwoven, plastics
surfaces, glass, ceramic, mineral building materials, such as molded
cement blocks and fiber-cement slabs, or metals, which in each case may
optionally have been precoated or pretreated.

[0171]Coating compositions of this kind are suitable as or in interior or
exterior coatings, i.e., in those applications where there is exposure to
daylight, preferably of parts of buildings, coatings on (large) vehicles
and aircraft, and industrial applications, utility vehicles in
agriculture and construction, decorative coatings, bridges, buildings,
power masts, tanks, containers, pipelines, power stations, chemical
plants, ships, cranes, posts, sheet piling, valves, pipes, fittings,
flanges, couplings, halls, roofs, and structural steel, furniture,
windows, doors, woodblock flooring, can coating and coil coating, for
floor coverings, such as in parking levels or in hospitals and in
particular in automotive finishes, as OEM and refinish.

[0172]Coating compositions of this kind are used preferably at
temperatures between ambient temperature to 80° C., preferably to
60° C., more preferably to 40° C. The articles in question
are preferably those which cannot be cured at high temperatures, such as
large machines, aircraft, large-capacity vehicles, and refinish
applications.

[0173]In particular the coating compositions of the invention are used as
clearcoat, basecoat, and topcoat material(s), primers, and surfacers.

[0174]It is an advantage of the polyisocyanate compositions of the
invention that they maintain the color stability of polyisocyanate
mixtures over a long time period in the presence of urethanization
catalysts.

[0175]Polyisocyanate compositions of this kind can be employed as curing
agents in coating materials, adhesives, and sealants.

[0176]By virtue of their low color number and high color stability they
are of interest more particularly for coating compositions for clearcoat
materials. Refinish applications are more particularly preferred.

EXAMPLES

[0177]In the examples and the reference examples, the substances used were
as follows:

Polyisocyanates A

Polyisocyanate A-1:

[0178]Polyisocyanate A-1 was prepared as follows:

[0179]1,6-hexamethylene diisocyanate from a phosgene process was stirred
in the presence of 0.7% by weight of 2-ethylhexanol at a temperature of
95° C. for 90 minutes. Subsequently 65 ppm by weight of
(2-hydroxypropyl)-N,N,N-trimethylammonium 2-ethylhexanoate were added as
catalyst for the trimerization, and the batch was left to react at
65° C.

[0180]At an NCO value of 40.5% by weight of the reaction mixture, the
reaction was discontinued by addition of 150 ppm by weight of
2-hydroxyethyl carbamate. The excess monomeric isocyanate was removed by
vacuum distillation at 145° C. Measurement data of the pure
compound: color number=23 Hz; NCO content=21.0%; viscosity=3100 mPa*s.

[0187]The polyisocyanates A were stored in about 50% by weight with the
concentrations--indicated in the experiments--of catalysts (B),
phosphonites (C), phenols (D), in each case 10% strength by weight in
butyl acetate, and about 50% by weight of solvent (E) in tightly closed
screw-top vessels under nitrogen, in order to exclude air. Traces of air
cannot be excluded.

[0188]The % by weight figures are based on 100% total weight. The
concentrations of the compounds (B), (C), and (D) in ppm are based, in
the respectively undiluted state of the compounds (B) to (D), on the
total amount of polyisocyanate (A).

[0189]Storage takes place in each case at 50° C. in a forced-air
oven. The color numbers are measured directly (immediately before the
beginning of storage), and after storage for different time periods.

[0192]The results of the experiment show that the color drift in solvent
naphtha is significantly more pronounced than in butyl acetate, and that
the antioxidative stabilization by the compounds C-1 and D-1 is
significant.